Please explain mono

At this point I’d say half my collection of 8,000ish is mono recordings. 78’s, microgrooves, and some lps and 45s. If it was recorded in mono, it should be played back in mono. With repeating others about setup and cartridges (I use Miyajima carts and SUT for all mono playback), what hasn’t been mentioned is the room setup. I have 1 room setup for stereo and a separate for mono. In the mono room I have 8’ between the rear wall and the speaker and use open baffles. The result- the deepest soundstage you can imagine. While stereo imagery is impressive, it feels fake compared to mono imagery. In the mono room you at all about front to back. My point being, mono doesn’t really impress me in the stereo room - so if you have a setup already optimized for stereo, the setup may be the issue. 

The "Back to Mono" post by @russ69 is a reference to Phil Spector, who in the early-70’s had a batch of buttons made with that phrase emblazoned on them. There are pictures of Phil with John Lennon during the recordings of John’s Rock ’n’ Roll album in which Phil is wearing one.

The singer/songwriter/organist leader of the Garage Band known as The Lyres---whose given name is Jeff Conolly---went by the name Monoman. I have a bunch of their albums (on LP and CD), and saw them live in the late-80’s at Club Lingerie on Sunset Blvd. One of the most exciting live bands I’ve ever seen. The sound system at the venue was a mono one. 

@bdp24 makes an interesting point, most live events are mixed in a mono fashion (there is sometimes a little panning in the PA system, but it is primarily mono to ensure the audience hear the ‘same’ concert). So when you go to gig the ‘live’ sound is often mono, except in small venues or jazz clubs, whereas recordings of concerts are made I stereo. So both are great!

I enjoy listening to solo piano music (classical, jazz, etc) in mono.  I play records or CDs through my Pioneer SA-1000 (as a preamplifier) into my Alan Eaton 45 tube mono power amplifier with a vintage Soundcraftsmen 2640TX speaker.  To me, solo piano sounds great from one speaker.

I have a Benz Glider Mono and use it exclusively for playing mono recordings. Listen to Illinois Jacquet Swings the Thing, Verve 45 rpm Mono rerelease originally recorded 1956. You will likely understand the appeal of mono. It's a great experience, equal but different to listening to well recorded stereo music